PVA is a water-soluble resin, and has been used in a wide range of applications by taking advantage of its characteristics. PVA is a powder or a granular solid in its product form, and widely used in various processes and applications typically after being dissolved in water.
Because of the conception that PVA is used after being dissolved in water, there are not many studies of PVA with regard to its characteristics in a product solid form.
However, a method that measures the surface condition of a film-like PVA is proposed recently. An analysis of a PVA film immersed in a non-solvent low-molecular liquid has revealed formation of larger numbers of intermolecular hydrogen bonds near the surface of PVA (see Non-Patent Document 1).
Use as an additive for pharmaceutical tablets is an example of PVA being directly used in solid form without being dissolved in water. Pharmaceutical tablet, a form of pharmaceutical preparations, is typically produced by tablet-forming. With respect to the method of tablet-forming, a granule obtained by granulating a powder mixture obtained by mixing various additive components with an effective ingredient (active ingredient) as a medicament, or the powder mixture is charged directly into a mortar, and molded into the desired size and shape by being compressed with pestle. The molded tablets are optionally coated with, for example, a cellulose compound or sugar, as required.
Examples of the additive components contained with the active ingredient in pharmaceutical tablets include: excipients (a component with no physiological activity, added to appropriately bulk up the formulation), binders (a component added to bind powder particles of raw materials, and to control the mechanical strength of the tablet), disintegrants (a component added to facilitate release of the active ingredient by disintegrating the tablet through expansion by absorbing moisture in the body), and lubricants (a component added to improve the fluidity of the powder for easy compression molding).
Among these additive components, the binder particularly has large impact on tablet strength. When the binder is not appropriately selected, there are problems such as molding failure, and tablet breaking occur after molding. The binder also affects the dissolution rate of active ingredient. Since the active ingredient is not easily absorbed if the tablet does not disintegrate when entering body, both the storage strength and the dissolution control upon administration are important and compatibility thereof is required. Particularly, sustained-release preparations, which are controlled to dissolve over a long time, have been actively developed since sustained-release preparations can improve the compliance by taking the medication less frequently, and, or prevent side effects by making the fluctuations of blood concentration smaller.
For example, Paten Document 1 discloses a binder using a polyvinyl alcohol copolymer of a specific average particle size. The binder is described as being most suitable for orally disintegrating tablets (OD tablets), and most suitable for direct tableting.
Patent Document 2 discloses that a polyvinyl alcohol copolymer is used for sustained-release preparations, and controlling dissolution over a long time is achieved by using it.